The invention relates generally to power consumption and noise mitigation techniques for electronic devices. More particularly, but not by way of limitation, the invention relates to reducing or avoiding operational problems caused by power droops and electrical interference during touch-surface data acquisition operations in portable electronic devices that generate radio frequency (“RF”) pulses.
The use of touch pads and touch screens (collectively “touch-surfaces”) has become increasingly popular in electronic systems because of their ease of use and versatility of operation. In general, these systems employ a two dimensional grid or array of sensing elements. Each sensing element (aka “pixel”) generates an output signal indicative of the electric field disturbance (for capacitance sensors), force (for pressure sensors) or optical coupling (for optical sensors) at the sensor element. The ensemble of pixel values represents an “image.”
In portable electronic devices such as mobile telephones and personal digital assistants (“PDA”) that use a touch-surface for user input and that also generate radio frequency (“RF”) pulses for communication, there is a problem in that touch-surface data acquisition cannot reliably or accurately occur during RF pulse transmission. This is primarily due to two factors. First, the power required to generate a RF pulse can cause a voltage drop large enough to interfere with the normal operation of a touch-surface's data acquisition circuitry. Second, the resulting RF pulse can generate sufficient electrical noise to interfere with the acquisition of touch-surface data.
Another complicating factor in devices of this type is the need to generate RF pulses at a rate that is more frequent than the time it takes to capture a complete image from the touch-surface. By way of example, mobile telephones conforming to the Global System for Mobile Communications specification (e.g., GSM 05.01, version 8.4.0) transmit RF pulses approximately every 4.6 milliseconds, with each pulse lasting 577 microseconds for voice transmission or 1,154 microseconds for data transmission. Touch-surface image acquisition operations, however, may take more the inter-pulse duration allowed by such specifications. Thus, it would be beneficial to provide a means to mitigate the operational interference to touch-surface data acquisition operations in portable electronic devices that generate RF pulses.